*D 300 F/11 diffraction too limited?*

Started May 16, 2008 | Discussions thread
OP Hide Takahashi Veteran Member • Posts: 4,234
Re: Diffraction and print size

monte12345 wrote:

Diffraction effects are independent of the camera resolution. They
have always been, what is happening now is that cameras have gained
enough resolution so that the effects are now quite visible in a 100%
peep. What has to be remembered is that it's the final magnification
of the image that determines if the effect of diffraction will have
an effect on the print. As camera resolutions increase, the effect
of diffraction will become visible in 100% peeps at wider and wider
apertures. So, at some point we'll all have to start to choose our
shooting aperture based on the intent of the image that we are taking
a picture of and quit worrying about what we see in a 100% peep.

So, what's all that mean? Simple, if you make a 4 x 6 inch print you
won't be able to see the effect of the diffraction of shooting at f22
because the magnification is too low to make the softness due to
diffraction visible in the print. Make a 24 x 36 inch print from
that very same shot and it will look terribly soft because the higher
magnification will make the effect of diffraction quite visible.

Now for some basic math and science. First, the human eye is only
capable of resolving about 6 to 8 lines per millimeter on a print at
12 to 18 inches without assistance. To give us a cushion, and
because I like round numbers, I'll use 10 ll/mm. Also, for those who
don't how to determine the total magnification of a print, it's
really quite simple, divide the vertical dimension of the print in
millimeters by the vertical dimension of the image sensor. (I use
the vertical because some print sizes have the ends of the image
cropped off, such as an 8 x 10 inch print). Also, there are 25.4
millimeters to an inch. so a 4 x 6 inch print measures 101.6 x
152.4mm.

Now for some math. BTW, I am basing the theoretical lens resolution
on Nikon's e-line table for resolution versus aperture. Which is as
follows.

f1.0 = 1560 ll/mm . . . 24 x 36 inch
f1.4 = 1072 ll/mm . . . 24 x 36 inch
f2.0 = 750 ll/mm . . . . 24 x 36 inch
f2.8 = 536 ll/mm . . . . 24 x 36 inch
f4.0 = 375 ll/mm . . . . 24 x 36 inch
f5.6 = 268 ll/mm . . . . 16 x 24 inch
f8.0 = 188 ll/mm . . . . 11 x 17 inch
f11 = 136 ll/mm . . . . . 8 x 12 inch
f16 = 94 ll/mm . . . . . . 6 x 9 inch
f22 = 68 ll/mm . . . . . . 4 x 6 inch
f32 = 47 ll/mm . . . . . . 3 x 4 inch
f45 = 32 ll/mm . . . . . . 2 x 3 inch
f64 = 24 ll/mm . . . . . 1.5 x 2 inch

So, keeping in mind that we want to achieve a resolution of 10 ll/mm
on the final print it's now easy to do the math. At f8, because
there are 188 ll/mm available in theory, we have to limit the total
magnification to 18.8 X. For the DX format that means that we
multiply 16mm by 18.8 to determine the vertical dimension of our
final print. (16 x 18.8) 25.4 = 11.84 inches so call it good for an
11 x 17 inch print. Which is how the above table was constructed.
Note, the table stops at 24 x 36 inches for the maximum print size
for one simple reason, even the very best Nikkors can only approach
theory at an aperture of f4.

Finally, we are making prints of pictures and not patterns of lines.
So we can cheat on those prints sizes in the above chart by quite a
bit. In general, I would consider a 50% increase in size quite
reasonable with proper post processing so shooting at f8 for a 16 x
24 inch print shouldn't be any problem. However, there is a limit to
how much we can "cheat" with Unsharp mask and that limit is probably
about at a 80 to 100% gain in size and going that far will be subject
dependent. So, in most cases trying to take a shot taken at f11 to
16 x 24 inches will be pushing the limit and may result in a print
that looks just a bit soft if it's examined closely. Which means
that you either hang your print so people can't look too close at it
or you just don't print that image that large. The simple fact is
that what we can see drops off with the distance. So if you have a
long viewing distance, you can make really big prints without anyone
complaining.

monte,

This IS a very useful table. When I shoot hummingbird with my D50, I can almost fill the frame so my hummer shot looks like a close-up shot. I printed a 12x18 at Costso and it came out beautifully. The shot was taken at f/13. Since the image is a close-up or near close-up,if I shoot hummingbird with the D300 at f/11,I may not see any diffraction in the 12x18 print. Just my guess.

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